The cutting of steel with torches has been available since the early 20th century. Typically these were oxy-acetylene torches and could cut steel up to twelve inches and more. Torches were hand held. During the 1960's, the torches were held by a machine which followed XY instructions in a simple geometric command language. This is known as “Numerical Control” or “NC”, and a NC machine moved the torch to cut simple shapes. This cutting is known as flame cutting or burning, and a representation of a typical modern single torch mechanical arrangement 10, including a single torch 12 and a NC Control 14, is shown in FIG. 1. In the 1970's, plasma arc cutting was introduced, which used ionized gas carrying an electric arc to melt the metal at very high temperatures. This was faster than oxy cutting at thicknesses up to one inch, and common piecing times were greatly reduced. Cutting technologies now include water jet and laser.
For steel cutting applications, it has been a desire of the marketplace to use the torches to cut the steel at an angle to the vertical and thus prepare plate edges for the next process in assembly, that of welding. This edge preparation is also known as beveling. As cut plate is often welded, a machine preparing weld ready components would save time in the manufacturing process. This beveling could eliminate a whole step of manual or semi manual edge preparation using grinders or small machines to result in saved time. Various beveling solutions have been developed over the years.
One solution is a triple head oxy acetylene torch 20 having three torches in an arrangement such as that shown in FIG. 2. With three torches 22 cutting a plate 24 simultaneously, a triple cut beveled edge is created in a single pass. Torches 22 are separated from plate 24, and it is important to note that while in principle these oxy heads can rotate endlessly, the gas supply hoses would wrap around the spinning head and practically limit the torches to one and one-half rotations in either direction. The spinning of the torches is required because of the use of three torches in plane. Use of a single torch does not require the spinning, and recent single torch holding devices do not spin. Not spinning has advantages and is generally desired. The triple torch solution is difficult to program, the center torch is always vertical (i.e., in line with a vertical tilt axis 26), and the overall solution has been very expensive.
To date, none of the beveling solutions have been fully satisfactory for a number of reasons. They have been generally too complex to operate, required drawings prepared in a special way, and/or took hours of manual programming to develop a bevel program, for example. A subtle problem was that the bevel information was separate from the part drawing and there was no simple way to communicate the required information regarding the weld preparation from the person who was qualified and authorized to supply the information to the NC programmer. “Weld preparation” refers to the preparation of an edge of a material for welding. For material over ¼″, weld preparation is typically necessary. Preparation usually involves a narrow area for hand welding, which is the weld root, and to allow access, grooves are often cut above and below the root gap.
Multi pass solutions using single torches have been attempted but were too complex to be practical. Machine developers have attempted to put the weld preparation parameters into the NC control language to make it easier to hand program for a single pass (or a double pass in some restricted cases), but multi pass bevels were still very difficult to program quickly or with any certainty. The production of multi pass parts has generally been impractical.
In 1991, the inventor of the advancement disclosed hereinbelow developed an earlier advancement that automatically added a single bevel angle to the industry standard DXF geometry files in common use. More particularly, layers were added to these DXF files to indicate a single ‘knife’ bevel and the angle of the bevel. While an automatic single pass system was an achievement, the DXF format is limiting because the only way to attach information to the movements was to use the layers described above. This worked, however, as practical assembly welding required only specific angles to be used. The layers were used to communicate many processes, but the welding information was limited to: CUT; CUT45; CUT-45; CUT40; CUT-40; CUT35; CUT-35; CUT30; CUT-30; CUT20; CUT-20; and CUTTRANSITION,
where CUT indicated the process type and the numeric part communicated the desired torch tilt. CUTTRANSITION was a special way of communicating a change area where various parameters could be changed such as torch tilt, torch rotation, kerf, and/or feedrate. Typically these areas would still have to be prepared manually with a grinder, as it was impossible to get into internal corners, for example. “DXF” refers to Drawing eXchange Format from AutoDESK, which has become the international defacto standard for two-dimensional shape transmission.
These layers were added by the drawing office, which effectively determined the subsequent assembly welding. These welds were described colloquially as either a knife bevel or a V bevel. The drawings also had to be created in such a way that the largest perimeter of the part was drawn. It could then be assumed that a positive torch tilt was cutting the top of the plate and a negative torch tilt was the line on the bottom of the plate. The torch path would then have to be offset by “plate thickness”*tan(φ) where φ is the torch tilt from vertical. This offset was handled by the NC control which interpreted the NC geometric instructions.
This prior art system saved time in manual preparation of parts for welding and has been in operation for around ten years. However, a knife bevel is far from satisfactory in many cases because the cost and time to weld such a surface is approximately double that associated with an “X” or double bevel. The ideal weld preparation for production (especially of very hard materials such as stainless steel) is a K bevel 30 as shown in FIG. 3, which is a triple pass bevel that eliminates the need for any grinding. K bevel 30 includes an undercut 31, a center cut 32, and a top cut 33 based on the plan dimension 34.
There have been many attempts to produce other beveling systems, most notably by the multi national companies ESAB and Messer Cutting & Welding. These systems can be made to work for a specific job, given enough time, but are overly complicated.
Most manufacturers (including ESAB, Messer, Farley, and Kinetics) have taken the approach of trying to put more intelligence in the NC control and adjusting the offset, kerf and feedrate with bevel tilt. ESAB has in fact put a nearly full weld profile definition (as shown in FIG. 4) in their NC language inside the NC control, albeit missing the critical root gap dimension. For this ESAB NC control: a) the drawings must be created using the maximum enclosing boundary (i.e., the “Max Top Bottom” view 55 shown in FIG. 5); and b) the torch is automatically offset by T*tan(φ) when a top bevel was used. Further, both feedrate and kerf are changed automatically inside the control with varying tilt angle A. Maximum enclosing boundary is also shown in FIG. 14, which depicts the six common dimension methods for a simple three-dimensional rectangle 1400: (a) maximum dimension 1402; (b) top dimension 1404; (c) dimension 1406 at mid thickness; (d) bottom dimension 1408; (e) minimum dimension 1410; and (f) dimension 1412 at specific depth 1414.
All known prior art beveling machines attempt to look after corners automatically, assuming a single pass bevel. All have an inbuilt orthogonal following mode where the rotation plane of the torch is automatically maintained at ninety degrees to the direction of travel of the torch. This is aimed at simpler manual or semi manual programming, not full automation with exact corner profiles for intersecting surfaces.
Existing systems from major manufacturers of steel cutting equipment by plasma or oxy acetylene appear to respectively utilize two types of beveling heads. The first is the triple head oxy machine which is used primarily for triple bevels (albeit with a fixed vertical dihedral). The second is the typically single pass plasma machine with a tilting and swiveling torch, which is generally termed a ‘chamfering’ unit by ESAB, which means that it is intended for a single pass bevel only. The ESAB programming example 60 shown in FIG. 6 indicates all the core aspects of chamfering a basic shape including the shape, ramps in and out of the movements, and the triangular corner, labeled as S1 through S9. The use of this chamfering unit to produce a multi pass weld preparation is known in the art, but as far as can be determined, this is largely a computer assisted manual process that starts with the original part program and requires additional information in another form on the edge preparation.
Another prior art programming example 70 from ESAB (now promoted as ESAB Expert Motion Plasma VBA with single path programming method) is shown in FIG. 7. Programming example 70 indicates the programming of a double pass bevel with aspects labeled S1′ through S14′; offset paths S3′ and S5′ create a double pass bevel section. Example 70 illustrates the use of the newly added weld profile inside the NC control, clearly intended to aid manual or automatic programming. What this means is that the addition of edge preparation information in prior art beveling systems is at the point of construction of the NC code (i.e., stage 803 in FIG. 8a). As such, this is done in a highly machine specific way and at best produces a library of NC parts which can be fabricated on a specific brand of machine and in fact a specific model within that brand range. These machines have changed over the last twenty-five years in their method of programming in the search for a simple way to create edge prepared parts using more intelligent NC controls and better programming systems.
In the processing of plates, the ability to place multiple parts on the one plate to be cut in the one operation is known as nesting. This adds a major layer of complexity to multipass beveling. In documentation readily available from Messer, a large German manufacturer with a long history of involvement in beveling and edge preparation, there is every indication that once NC programs are produced, the NC control has special commands for transformation of axes, including rotary axes which are aimed at allowing the nesting of raw NC part programs which include beveling detail. Their commands are recent extensions to their use of standard format EIA Word Address language generally used with the extensions of A and C. #MCS, #TRAF, #KIN and #CAX TRAX are commands which affect the coordinate systems and the associated bevel tilt, rotation, and orthogonal following.
Without specific detail, this indicates that rather than attempting to build the weld profile into the NC language as ESAB has done, Messer is trying to nest raw NC weld preparation programs directly into the NC control, which may result in problems in adjusting internal rotations and coordinates. In reference to FIG. 8a, Messer communicates NC programs to the nesting system, which means storage of parts is in a machine specific form. It also means they may not have the ability to avoid collisions in nesting. These approaches of nesting of NC code as in the Messer approach and placing weld profiles in the NC language as in the ESAB approach distinguish these approaches totally from the invention disclosed herein.